This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Electron transfer dissociation (ETD) can be used to provide unique and complementary fragment ions when compared to other dissociation techniques, such as collision induced dissociation (CID). Weak side chain bonds such as are observed at phosphorylated amino acids in peptides are often lost during CID, but preserved during ETD. This makes the technique useful for the detection and analysis of posttranslational modifications in peptides and intact proteins. This project is devoted to the development and improvement of ETD for such applications.